Low-field rheo-NMR: A novel combination of NMR relaxometry with high end shear rheology

Abstract

Time-domain NMR is a well known tool for assessing the molecular dynamics in soft matter by measuring the excitation and subsequent decay of 1H nuclear magnetization. It is widely used, e.g., to quantify the composition of heterogeneous soft matter systems like semicrystalline polymers or emulsions. Further applications, known from academic research and industrial application, include measuring the moisture content in solids, the residual magnetic dipolar coupling for quantifying molecular motion in crosslinked systems, or diffusometry. We report the integration of a permanent magnet based pulsed NMR spectrometer into a modern, commercially available high-end shear rheometer. The setup allows for the first time to simultaneously conduct time-domain 1H NMR and steady shear or dynamic rheological measurements on one sample and to directly correlate the results from both, without concerns about differences in the sample history or temperature calibration. Moreover, the new in-situ combination allows the full usage of the rheometer to apply nonlinear deformation, under steady shear or large amplitude oscillatory shear, and directly measure the effect on the time evolution of the sample properties. This publication introduces the technical setup of this novel instrument combination and describes the shear induced crystallization of polyolefins to demonstrate its capabilities. Further potential applications are outlined.

Polymer crystallinity and crystallization kinetics via benchtop 1H NMR relaxometry: Revisited method, data analysis, and experiments on common polymers

“…Compared to DSC, 1 H NMR relaxometry is better suited to the study of slow crystallizations as it does not require peak integration. Furthermore, the non destructive nature of 1 H NMR relaxometry allows for the performance of in situ experi ments in combination with applied flow or pressure to achieve better insight into how these parameters affect polymer crystalli zation [28,29]. Fig.…”

Polymer Crystallization Studied by Hyphenated Rheology Techniques: Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy

“…The hyphenated low‐field Rheo‐NMR set‐up is based on a portable 1 H NMR unit ( B 0 = 0.7 T, ω L /2π = 30 MHz for 1 H) that was integrated into a commercial strain‐controlled TA/Rheometrics ARES shear rheometer (Figure a) . The NMR magnet consists of a Halbach array of 92 NdFeB permanent magnets with a Dewar between the temperature‐sensitive permanent magnets and the sample space to achieve good thermal insulation.…”

“…Techniques that characterize molecular dynamics and consequently probe local molecular conformations were also combined with rheology. These set‐ups are based on dielectric spectroscopy and NMR relaxometry, and can be used to investigate the origins of macroscopic flow behavior in soft matter. Further hyphenated rheology techniques that do not belong to any of the three main categories listed above are based on calorimetry, dilatometry, or electrical conductivity .…”

“…The flow and deformation behavior of polymer melts can be thoroughly studied using rheology, whereas low‐field NMR relaxometry (also called Time Domain (TD)‐NMR) is a powerful technique for the characterization of molecular dynamics in polymeric materials . To achieve a substantial insight into the interplay of these domains, especially under flow, these two methods were combined into a single set‐up (Figure a) . This approach is different from other Rheo‐NMR set‐ups, as its main purpose is the study of molecular dynamics rather than chemical structure via NMR spectroscopy or morphology via magnetic resonance imaging.…”

Rheo‐NMR in food science—Recent opportunities

“…However, torque and NMR data could be acquired successively (much in the spirit of the work cited above) using the same shear geometry, yielding NMR relaxation data, or 1D velocity profiles across the sheared material in addition to the separately measured shear stress. Later developments lifted this limitation, now providing low field Rheo‐NMR accessories that can be fitted to commercial rheometers, providing simultaneously the capabilities of high end rheometry coupled with NMR relaxometry …”